Because of the characteristic properties of natural rubber, such as large elongation, high elasticity, high tensile strength, good cohesive strength and the like, it has been used in various fields ranging from industrial articles including automobile tires, belts and adhesives to household articles such as gloves, as well as nursing tools, contraceptives and the like.
Since natural rubber is produced by collecting the rubber from natural rubber latex by coagulation and further carrying out various operations such as mastication, blending of various compounding ingredients, molding, vulcanizing and the like, it contains non-rubber components such as protein and the like as impurities originally contained in natural rubber latex.
Since kinds and quantity of such protein vary depending on the locality and production season of natural rubber latex, it causes variations in the quality, vulcanizing characteristic and the like of natural rubber and reduces mechanical characteristics such as creep characteristic, aging resistance and the like mechanical characteristics and electric characteristics of natural rubber such as insulation and the like electric characteristics of natural rubber.
In addition, it has been reported in recent years that dyspnea and anaphylactic symptoms (vascular edema, urticaria, collapse, cyanosis and the like) seemingly caused by the protein in natural rubber were induced by the use of medical tools made of natural rubber, such as surgical gloves for operation use, various types of catheter, masks for anesthesia use and the like.
In order to resolve these problems, attempts have been made to remove protein by concentrating natural rubber latex after washing with water, adding a surfactant if necessary, or by decomposing protein with a proteolytic enzyme.
These prior art methods, however, are not effective in sufficiently removing protein contained as contaminant in natural rubber latex.